Gesellschait



Patented July 18, 1933 UNI-TED STATES- PATENT OFFICE HEB-HAHN LANG, OIPIESTRI'I'Z nrz. mnn-on-m-smn m wrnrmmr mum,

or wirrmime, em, assrenons re 1. at rmnmnus'rm Amres'smscmr, orrmn-onr-on-rnn-mm, enmity mrrrcarron or mnc'raonms Io 'DrawlnglApplication fledIune 27, 1980, Serial lo. 464, and in Germany I'm 28,1029.

The present invention relates to improvements in the elimination ofcontaminating substances from electrolytes by means of an electrolytictreatment and is-more especially concerned with the separation of suchconizaminations which are present in the electroentally converted intosuch form under the influence of the electric current.

-When carrying out electrolytic purification of electrolytes in theusual manner, namely by subjecting animpure electrolyte between an anodeand a cathode of. usual shape and form to the action of a current, it iswell known that the current yield, and also the energy yield relative tothe contaminating substance are both ra idly diminished below a certainlimit 0 its concentration" in the solution. It is therefore generallyconsidered inadvimble to pursue the electrolytic purifying treatmentbeyond a certain limit of concentration, asthe process under theconditions resulting therefrom can no longer be effected in aneconomical manner.

The main object of the present invention therefore is to provide a ethodfor improving the current as well 2 the energy yield of electrolyticpurification in cases when the contaminations are present in theelectrolyte only in exceedingly small concentrations, ranging from aboutone tenth of one percent down to mere traces. The invention aims torender the usual process economical even in extreme cases by suitably adusting the working conditions of the process. The method according tothe present invention is equally applicable to the purifying treatmentof saline as well as caustic or acid solutions containing either smallamounts of contaminating heavy metal salts or compounds which under thedirect or indirect action of the current are reduced to the metallicstate, and also contemplates the conversion of'contaminating compoundsinto a state of higher or lower valency.-

According to the present invention the electrolyte containing thecontaminations is caused to flow not alo but through the electrode orelectrodes dfiecting the deposition or conversion of the contamination,said active electrode or electrodes for this purpose being provided withextremely narrow assages which are permeable to the liqui The width ofthese passages is so either in an ionized form or are inciselected as tostand in a ratio to the concentrodes are preferably made of an extreme--ly dense wire netting, having a mesh density of at least about 100 persquare centimetre,

the erman and French languages) being especially suitable. The speed ofthe flowin electrolyte is also extremely small and a vantageouslg onlyamounts to a few centimetres per our.

As to the current density imposed upon the active electrode, itv isadvantageous to adjust the same to the low concentration of theimpurities to be removed from the electrolyte.

The current densities required for the purpose are, in any case,considerably below the densities generally usual foiperformingelectrolysis on a technical scale, said processes making use, as a rule,of as high densities as plossible for thepurpose of decomfication may beloaded with any ordinary current density.

The following examples show various particular modes of application ofthe present invention.

(1) Elimination of arsenic from phosphm'io Phosphoric acid having a H,POcontent of to percent and containing, besides traces of heavy metalsalts, about 20 milligrams of A150, per litre,"is passed'at a multiilewire nettings (called Tresse in.

speed of about 4' centimetres per hourthrough a trough-shaped oblongcontainer of suitable material, in which is spanned a' number of copper'wire nettings extending.

over the whole cross-section of the trough, the fabric of said nettingsbeing densely meshed (for instance, 450 meshes persquare centimetre,diameter of the warp-wires 0,17 millimetres diameter of the weft-wires0,25 millimetres}. Between each pair of the nettings switched inparallel, one or more platinum wires serving as anodes are suspended inthe electrolyte and a direct current of low voltage, say about 2 or 3volts, is passed 5 .through the bath. On the anodes which are chargedwith about'0,1 ampere per square centimetre, a moderate discharge ofoxygen takes place owing-to the decomposition of water. On the cathodewire nettings which are loaded with a current density amounting to onlyabout one hundredth to one thousandth of that on the anodes, a dischargeof the heavy metal ions takes place and, simultaneously, the arsenousacid is reduced to elementary arsenic, the metals and the arsenic beingprecipitated in a loose metallic state on the cathode and being sweptalong bythe phosphoric acid in form of an extremely fine suspension.After having passed the cathode wire nettings in series, theprecipitates are removed by filtration from the acid, which nowrepresents a perfectly clear pure liquid entirely free from foreignmetals and from arsenic.

The following t'bles show the economy of the process according to theinvention with regard to the current yield as compared with similarpurification processes in which the electrolyte is not caused to ass theelectrode. (See tables 1 and 2.) he figures in the first column of thesetables refer to amperes per square centimetre of the entire cathodesurface (not considering the aperture of the meshes).

It convincingly appears that the current consumption per kg P 0 whenworkin according to the invention is at least ten tlmes smaller andfurther that the influence of a reduction of the current 40 density onthe cathodes is more pronounced, than in processes desisti'n frompassing the eletrolyte through the e ectrode. In fact, the currentconsumption in the present case closely approaches the theoretical, aswill appear from the course of the respective figures in correlation tothe current density. Probably this favourable result is also due to'thefact that the meshes of the wire netting are still somewhat narrowed bya temporary fixation of some of the arsenic-pm cipitated duringelectrolysis.

.'In a similar manner, also other electrolytes containing small amountsof substances which are either electrolytically separable or 5 may atleast be influenced electrolytically, may be purified. Thus it hasappeared from experiments that the oxidation of small quantities of HPO, and H PO such as frequently occur in phosphoricacid produced bvarious methods, takes place with a consi erably improved current yield(6 to 10 times better), when the solution is assed through extremelyfinely meshed an e wire nettings (5,000 meshes per square centimetre)instead of coarser nettings (100 from these figures I meshes per squarecentimetre), the current density, which is kept small, in both casesremaining constant. It thus appears that in the process according to theinvention, also both the anode and the cathode may serve as activeelectrodes, either simultaneously or or consecutively.

(2) Elimination of ansenic from sulphuric Sulphuric acid of 1,68 sp; gr.containing 1,47 grs. of arsenic per kg was passed through a platinumwire netting of 10,000v

meshes per square centimetre serving as a cathode and through perforatedlead sheets Table I 1.-Pwri7ication of phosphoric acid (65 percent P 0containing 0.023 pencent of arsenic Electrolyite E t I is passe ac to ythrough ff f Electrolyte vividly wire net 8] p win ispassed' stirred byting oath ggg along sheet rotating odes accordcathodgs cathodes wirenetting Current load w cathode amps persq, invention 'Cur- Cuf- On!Ourrent rent B rent 33 rent 33 yield Q yield 2; yield kg yield kg rrperpernt 3:111; cent cent The current Table,2.-Purification of phosphoricacid I (65 per cent P 0 containing 0.001 percent of arsenic Electrolyteis Electrolyte nimu li Electrolyte vividly wire net we lspassed stirredby ting catha along sheet rotating odesaceord- 5 cathodes wlrenettmgCurrent 1000' 8 2 08mm amps persq invention Cur- Cur- Cur- Current Kwhsrent Kwhs rent rent a yield yield yield e yield 0 1 r i) Pi) P cent"cent "cent "cent When on the other hand, the acid, instead ofbemg'passed through the electrodes, is sub ected to electrolysis whileremaining stationary, the current consumption required to attain thesame stage of purification amounts to 5.43 ampere hours for every onekilogram of sulphuric acid, this corresponding to a current yield ofonly28 percent.

(3) Elimination of zgikenioaaid from acetic Acetic acid (50%) containing0.01 gr As O per kg was passed through a platinum wire netting of about10,000 meshes per square centimetre serving as a cathode with a speed ofabout 1 centimetre per hour. The anode consisted of platinum wiressuspended in the electrolyte. The cathodic current density amounted to0.0001 ampere per square centimetre. After consumption of one amperehour per kg the acid was found to be free from arsenic. The currentyield amounted to 1 percent.

When the test was carried out by passing the acetic acid along insteadof through the cathode, all the other conditions remaining unaltered, 8ampere hours were required to attain the same degree of purity, thecurrent yieltd thus corresponding to only 0.12 percen (4) Elimination ofmrmuy} from acetic acid Acetic acid (50%) containing 0.01 gr of mercuryper kg was passed through a platinum wire netting of 10,00 meshes persquare centimetre serving as a cathode, with a speed of 1.3 centimetresper hour, platinum wires suspended in the electrolyte serving as anodes.The cathodic current density amountfying meth ed to 0.0001 ampere ersquare centimetre. After consumption 0 0.24 ampere hour per kg of aceticacid, the acid was free from mercury, this corresponding I to a currentyield of about 1.1 percent.

When the acid is simply assed along instead of through the cathodenetting, all of the other conditions remaining the same, the completeelimination of the mercury can onlybe effected with a current yield ofabout 0.15 percent.

It appears from the Examples 2 to 4 that even with comparatively lowcurrent yields 'the method according to the present invention still comares favourably with the puris formerly employed.

, eliminate small quantities of lead The process as described is alsoapplicable to the purification of other electrolytes as long as thelatter, under the current densities required for the elimination of theimpurities, do not themselves undergo an alteration. Thus for example itis possible to rom nitric acid or nitrate solutions, if desired also assuperoxide of lead on the anode.

We claim:

1. In a process for purifying by electrolysis an electrolytefromimpunties dissolved therein, the steps which comprise passing said,impure electrolyte through a meshed wire cathode and charging saidcathode with a current density of at most one hundredth of the anodiccurrent density.

2. In a process for purifying by electrolysis an electrolyte fromimpurities dissolved therein, the steps which comprise passing saidimpure electrolyte through a meshed wire cathode with a speed of at mosta few centimetres per hour and charging said cathode with a currentdensity of at most one hundredth of the anodic current density.

3. In a process for purifying phosphoric acid from impurities dissolvedtherein, the steps which comprise passing the raw phosphoric acidsuccessively through a series of meshed wire cathodes and charging saidcathode with a current density of at most one hundredth of the anodiccurrent density.

4. In a process for purifying phosphorlc acid from impurities, dissolvedtherein, the

steps which comprise passing the raw phosphoric acid successivelythrough a series of meshed wire cathodes with a speed of at most a fewcentimetres per hour, and charging WILHELM MI jLLER. HERMANN LANG.

